The invention discloses a safety cap made of plastic material, particularly suited to be applied on bottles containing medicines or other potentially dangerous substances. The cap according to the invention belongs to the type of caps, which are usually called "child-proof", i.e. those caps which, in order to be unscrewed, need the logical co-ordination of certain movements. In other words, said movements can only be voluntarily performed by persons who are perfectly aware of what they are doing.
Some safety caps are known, consisting for instance of two elements, wherein the inner element is screwed on to the cap and the outer element is co-axial with the inner element and is connected with it. With this type of cap, the tightening action is always possible, while the unscrewing action, which gives access to the bottle's content, is only possible if pressure is applied axially to the outer element against the inner element and the cap is unscrewed at the same time. Generally, these types of caps present the inconvenience that the bottles suited to receive them must present an indented ring around the neck, so that a seal can be applied on the bottle and this complicates the manufacture of the bottle itself, because of the presence of undercuts. Moreover, it must be underlined that the safety of the cap is fairly limited, since it is possible that the opening action may be performed by unauthorized persons through the involuntary but co-ordinated actions of axial pressure and simultaneous unscrewing.
The European Patent EP 0 184 795 has been registered in the name of the author of the present invention. This patent overcame the above-mentioned inconveniences by disclosing a cap consisting essentially of three parts, i.e. of an inner element screwed on to the neck of the bottle, of an outer cylindrical element co-axial with the inner element and of a push button placed between the inner and the outer elements. The presence of suitable cogs between the outer and the inner elements allows the caps to be tightened around the bottle under any circumstance, while the untightening of this cap is only made possible by pressing the push-button placed between the outer cylindrical element and the inner one and by simultaneously untightening the outer element. This is made possible by the fact that the pressure of the push-button against the bottle causes the rigid connection between the inner and the outer elements, so that the untightening of the latter element drags also the inner element.
Although this previous cap grants an optimum degree of safety, it has been noticed that it can be fairly difficult even for persons who are able to use this type of caps to untighten this cap while keeping constantly depressed the push-button connecting the outer element with the inner element, particularly if the cap is screwed very tightly around the container.